Mid 19th century metric chain

I bought this chain on an on-line auction site in 2005. I wanted to have one to use it for educational purposes and, together with the imperial chain and steel tapes in my collection, it is regularly used that way. The chain came from a French seller, is signed "LB" between the pans of a balance and "décamêtre". The latter indicates that it probably is of French origin, which also explains its whereabouts before I bought it. The initials "LB" between the pans of a balance may have been the signature of Lerebours, a French instrument maker from Paris. The chain occurs in their 1853 catalogue, albeit without reference to this signature, and both the chain and a similar signed steel tape occur in a catalogue from the first decade of the 20th century by their successor Secrétan à Paris, again without reference to the signature.1,2

The chainThe chain is made of steel, 10 metres in length and made of 20 centimetres links. The links are joined together with rings, every fifth of which is made of bronze, while the rest is made of the same steel as the links themselves (see figure 1). At the centre of the chain half a link is suspended from the bronze ring to indicate 5 metres (see figure 4). The handles do not have a groove for the ground pins, which may be explained by either the early provenance or the intended use (i.e. for measurements of lower accuracy).3 They consist of a bronze plate with three holes, two of which have the steel loop of the handle riveted into is, while the third and middle one holds the start of the chain. On the bronze plate the signature and the "décamètre" are stamped in (see figure 5), the latter indicating that the chain is 10 metres in length, which includes the handles completely at both ends.

Figure 2: At the upper left and upper right the shiny bronze rings are clearly visible.

Use and diffusionThe chain is one of the longest-in-use instruments in surveying. The first mention and depiction of a survey chain - or at the time so called "wyer line" - dates from 1590 and can be found in the work A Treatise Named Lucar Solace by Cyprian Lucar.4

Although the use of chains seized in the 1960s in the 'Western World', the chain is still in continual use outside it. An Indian textbook on surveying that was first published in 1999 still spends a paragraph and two pages with drawings on the chain. The author wrote that

"Chains are used to measure distances when very great precision is not required. In our country [India] it is frequently used though in other countries it is being gradually replaced by tapes. [...] In India link type surveying chains of 30m lengths are frequently used in land measurement.".5

The textbook was written "...to be an introductory text for the first course in surveying for the engineering students ... of civil, architecture and mining engineering ... [and] ... will also be suitable for professional courses in surveying.".6

Figure 3: The handles of the chain are attached to shorter links and are included in the overall length.

Chains have been made in imperial (like the Chesterfield one in my collection) and metric units. A set of 11 or 6 ground pins would have been used with the chain to count the sections measured with it. The fore man would have all pins at the start of the measurement, pushing one in the ground every whole length of the chain. The rear man would pick up the pins as they go. As soon as the fore man had no pins left, both men came together to exchange pins and they knew that another section of 10 or 5 chain lengths had been measured.7

AccuracyAlthough seemingly simple instruments, chains could produce very accurate results and were preferred above angle measurement devices up to the 18th century.8

In 1810 Nesbit wrote his first edition of a textbook on surveying, which would be continuously updated and reprinted well into the 20th century. The first edition did not contain any reference to the theodolite, which he explained in the 1820 second edition by stating that

"As the theodolites is sometimes used in surveying Meres, Woods, Roads, Rivers, and Canals, when angles cannot be taken by the Chain, I have given a description of this instrument; but as neither it nor the Plane Table are ever used by Professional Surveyors, when they can avoid it; and as this Treatise is confined chiefly to Chain surveying, I have not given any directions for measuring either with the Plane Table or the Theodolite. Besides, the expense of these instruments places them out of reach of a great number of those persons...".9

A year later a chain by Throughton was used to measure a two mile stretch over ice. The measurement was repeated and found to be within one inch of the first result, which is a repeatability of 1:127,000 or 8mm/km!10 As indicated above chains were gradually replaced by steel tapes, like the ones by Tibaut Desimpelaere and Ahrend and in my collection.